Planar rotor-enabled quenching-resistant NIR-II fluorophores for high-contrast bioimaging and efficient cancer phototheranostics

Quenching-resistant near-infrared-II (NIR-II) fluorophores with strong light harvesting capabilities and excellent photophysical properties remain a critical challenge in cancer phototheranostics. Herein, we report a novel acceptor–donor–acceptor (A–D–A) fluorophore, BTP-2TCF, constructed by introducing planar, rotatable tricyanofuran (TCF) acceptors into the core of the high-performance dye Y6. This molecular design imparts obvious anti-quenching behavior to BTP-2TCF nanoparticles (NPs), achieving an improved photoluminescence quantum yield of 1.9% and over a ten-fold enhancement in reactive oxygen species generation compared to Y6 NPs. These improvements are likely attributed to the restricted intramolecular motion of the TCF rotor, which suppresses non-radiative energy dissipation. BTP-2TCF NPs also exhibit a high molar absorption coefficient (>82 000 M⁻¹ cm⁻¹) and brightness (635 M⁻¹ cm⁻¹), outperforming conventional anti-quenching dyes. Their bright NIR-II fluorescence enables high-contrast visualization of mouse vasculature. Guided by NIR-II fluorescence imaging, BTP-2TCF NPs demonstrate superior photodynamic and photothermal anticancer efficacy in vivo. This study highlights the TCF planar rotor as a powerful strategy for developing next-generation quenching-resistant fluorophores for biomedical applications.